1. Field of the Invention
The present invention relates generally to a concentric machining device, and in particular, to a device and method for machining the outer circumferential surface of an optical communication ferrule or a cylindrical body having a fine inner diameter of 200 .mu.m or below, setting an inner circle concentric with an outer circle.
2. Description of the Realted Art
Concentric machining refers to machining a cylindrical body having an inner circle and an outer circle so that the outer circle is concentric with the inner circle. For the concentric machining, a pin or a wire is inserted into a fine inner diameter.
In a conventional concentric ferrule machining system, for concentric machining of ferrules, a wire is inserted into the inner diameter of the plurality of ferrules, both ends of the wire are fixed to fixtures, a tensile force is applied to the wire, and then the outer circumferential surfaces of the ferrules are machined using a polishing wheel.
To concentrically machine a cylindrical body having an inner diameter and an outer diameter, a steel wire processed with high precision is inserted into the inner diameter of the cylindrical body and an outer circumferential surface of the cylindrical body is machined by a predetermined amount by a polishing wheel, with the center of the inserted wire set as the center of the inner diameter of the object. Thus, the different inner and outer diameters become identical after machining the outer circumferential surface of the cylindrical body concentric with the center of the inner diameter.
However, the conventional machining method has some problems in machining range and precision:
(1) Wires are seldom, if ever, suitable for a very small inner diameter. Even such a wire does not withstand a tensile force applied to both ends thereof in concentric machining of a machining object due to the too small inner diameter. PA1 (2) Concentric machining is impossible if an inner circle of a machining object is tapered or in an irregular shape, due to a varied inner diameter. PA1 (3) There is a limit to increasing precision. Here, if an insertion margin between the inner diameter and the wire is 0.3 .mu.m and the machining precision of the wire is 0.2 .mu.m, the machining precision of the inner diameter is 0.5 .mu.m. Therefore, a maximum error of 1 .mu.m can occur and the machining object is not suitable for precision machining. PA1 (4) The friction between an inner circumferential surface of a machining object and a wire inserted into the inner diameter of the machining object is likely to scratch or deform the inner circumferential surface. PA1 (5) In concurrently machining a plurality of ferrules by insertion of a wire, possible introduction of foreign materials between the ferrules induces errors, thereby making precision machining impossible.
Examples of methods of the conventional art relevant to machining cylindrical bodies or making of ferrules are seen in the following U.S. Patents.
U.S. Pat. No. 4,721,357, to Kovalckick et al., entitled Methods Of And Apparatus For Reconfiguring Optical Fiber Connector Components And Products Produced Thereby, describes an apparatus for reconfiguring a connector for plugs terminating a fiber optical cable. The method involves rotating the plug while passing light through the optical fiber to determine the direction of the axis of the optical fiber and then making adjustments to make the center of the fiber core coincident with the axis of rotation.
U.S. Pat. No. 5,111,571, to Ciboldi et al., entitled Method For Manufacturing A Body With A Surface Of Revolution At Its End With The Axis Thereof Aligned With An Axis Of The Body, describes an apparatus for making a ferrule for expanded beam connectors in which the ferrules have a surface of revolution in the form of a tapered cavity. During removal of material, mechanical compensating forces determined by transverse movements of the shaft of the body are applied to prevent such transverse movement.
U.S. Pat. No. 5,734,768, to Kim et al, entitled Aligning Apparatus For Optical Coupling And Manufacturing Method Thereof, describes a ferrule for an optical fiber coupling.
U.S. Pat No. 5,802,937, to Day et al., describes an apparatus for machining surfaces to nanometer accuracies. Current is measured through the cutting tool and the workpiece, and the cutting tool is displaced to maintain the current flow at a constant level.
U.S. Pat. No. 5,909,530, to Ohkubo et al., entitled Method For Manufacturing Ferrule For Use With Optical Fiber Connector, describes a method for manufacturing a ferrule including an outside diameter grinding step using the both center method.
U.S. Pat No. 5,918,196, to Jacobson, entitled Vision System For Analyzing Solid-of-Revolution Radius Profile, describes a method for visually monitoring the radius of an item rotating about a fixed axis. The method includes steps of acquiring an image of a circumferential feature of the solid using a camera, and determining the equation of an ellipse that substantially fits a set of points along the image of the feature. The patent, however, does not discuss using the data to accurately machine ferrules.
These patents, however, do not address the problems discussed above. Therefore, based on my reading of the art, I believe that what is needed is an improved method for concentric machining of cylindrical bodies with small internal diameters.